1. Field of the Invention
The present invention relates to a temperature sensor circuit, and more particularly, to a temperature sensor circuit in which influence of nonlinear characteristics is eliminated.
2. Description of Related Art
There is known a temperature sensor circuit that includes a temperature sensor to measure a temperature. For example, Japanese Patent Application Publication (JP-A-Showa 56-135963: related art 1) discloses a semiconductor integrated circuit for a temperature sensor. FIG. 1 is a circuit diagram illustrating a configuration of the semiconductor integrated circuit for the temperature sensor in the related art 1. The semiconductor integrated circuit for the temperature sensor includes a temperature sensor (junction transistor for the temperature sensor) 103 using a first conductive type of substrate as a collector, a second conductive type of a diffusion layer as a base, and the first conductive type of a diffusion layer formed in the second conductive type of the diffusion layer as an emitter; and a constant current source (complementary insulated gate field effect transistor type constant current circuit) 102 present within the same substrate, and is characterized by defining a base-emitter voltage of the temperature sensor 103 as a temperature detecting voltage.
In the semiconductor integrated circuit of the related art 1 illustrated in FIG. 1, an output voltage V0 is expressed by the following equation (100) on the basis of forward voltage drop characteristics of a diode:
                                                                                             V                  ⁢                                                                          ⁢                  0                                =                                ⁢                                                      kT                    q                                    ⁢                                      ln                    ⁡                                          (                                              Id                                                  I                          S                                                                    )                                                                                                                                              =                                ⁢                                                                            k                      q                                        ⁢                    T                    ⁢                                          {                                                                        ln                          ⁡                                                      (                            Id                            )                                                                          -                                                  ln                          ⁡                                                      (                            b                            )                                                                          -                                                  m                          ·                                                      ln                            ⁡                                                          (                              T                              )                                                                                                                          }                                                        +                                      Eg                    q                                                                                                                                          ⁢                                  [                                                            ∵                                              I                        S                                                              =                                                                  bT                        m                                            ⁢                                              exp                        ⁡                                                  (                                                                                    -                              Eg                                                        kT                                                    )                                                                                                      ]                                                                                          (          100          )                    where q is an elementary charge, k is a Boltzmann constant, T is absolute temperature, Is is a saturation current, b is a proportional constant, m is a saturation current temperature coefficient, and Eg is a bandgap energy.
As expressed by the equation, there exists a nonlinear term “−m×ln (T)” of a voltage with respect to the temperature T. FIG. 2 is a graph illustrating a relationship between the temperature and the output voltage in the above-described semiconductor integrated circuit for the temperature sensor. A vertical axis represents the output voltage V0, and a horizontal axis represents the temperature T. Also, a solid line B represents a curve expressed by the above equation (100), and a dashed line A represents a straight line (linear line) partially coming into contact with the solid line B. In the above equation (100), m is not essentially equal to zero (m≠0). For this reason, as illustrated in FIG. 2, the solid line B loses touch with the dashed line A while partially coming into contact with the dashed line A. That is, the output voltage V0 has a nonlinear voltage error with respect to the temperature T. In high accuracy measurements in which a voltage error becomes significant, the voltage error has been corrected mainly by a multipoint calibration. Therefore the related art 1 leads to increase in cost. Accordingly, there is desired a technique capable of detecting a temperature with lower cost and higher accuracy.